Energy is one of the imperative global issues because of the escalating demand for, but depleting supplies of, fossil fuels. Numerous sustainable alternative energy resources have to be explored to alleviate the world's dependence on fossil fuels and lessen the negative environmental impact from their combustion. Recently, the renewable osmotic energy produced from the pressure-retarded osmosis (PRO) process has attracted great attention because of its huge energy potential, clean technique (zero carbon dioxide emission) and high stability as compared to solar or wind. This process harvests energy by exploiting the osmotic pressure gradient as a driving force across the membrane to induce water transport from the freshwater side towards the salty water side. The pressure built up within the salty water chamber can be released to spin an integrated turbine for electricity production.
One of the main barriers to commercialize the PRO process is the membrane because it is the heart of the entire process. To date, a commercially viable membrane able to sustain high pressures required for power production by the PRO process is not yet readily available. In literature during the past decade, PRO membranes have been developed in the configuration of inner-selective thin-film composite (TFC) hollow fiber membranes, where the thin selective film is formed on the lumen surface of the hollow fibers. In this way, the salty water is pressurized into the lumen side while the fresh water is circulated around the shell side of the fiber.